CfA: Some Stars Capture Rogue Planets

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CfA: Some Stars Capture Rogue Planets

Post by bystander » Tue Apr 17, 2012 6:25 pm

Some Stars Capture Rogue Planets
Center for Astrophysics | 2012 Apr 17
New research suggests that billions of stars in our galaxy have captured rogue planets that once roamed interstellar space. The nomad worlds, which were kicked out of the star systems in which they formed, occasionally find a new home with a different sun. This finding could explain the existence of some planets that orbit surprisingly far from their stars, and even the existence of a double-planet system.

"Stars trade planets just like baseball teams trade players," said Hagai Perets of the Harvard-Smithsonian Center for Astrophysics.

The study, co-authored by Perets and Thijs Kouwenhoven of Peking University, China, will appear in the May 1st issue of The Astrophysical Journal.

To reach their conclusion, Perets and Kouwenhoven simulated young star clusters containing free-floating planets. They found that if the number of rogue planets equaled the number of stars, then 3 to 6 percent of the stars would grab a planet over time. The more massive a star, the more likely it is to snag a planet drifting by.

They studied young star clusters because capture is more likely when stars and free-floating planets are crowded together in a small space. Over time, the clusters disperse due to close interactions between their stars, so any planet-star encounters have to happen early in the cluster's history.

Rogue planets are a natural consequence of star formation. Newborn star systems often contain multiple planets. If two planets interact, one can be ejected and become an interstellar traveler. If it later encounters a different star moving in the same direction at the same speed, it can hitch a ride.

A captured planet tends to end up hundreds or thousands of times farther from its star than Earth is from the Sun. It's also likely to have a orbit that's tilted relative to any native planets, and may even revolve around its star backward.

Astronomers haven't detected any clear-cut cases of captured planets yet. Imposters can be difficult to rule out. Gravitational interactions within a planetary system can throw a planet into a wide, tilted orbit that mimics the signature of a captured world.

Finding a planet in a distant orbit around a low-mass star would be a good sign of capture, because the star's disk wouldn't have had enough material to form the planet so far out.

The best evidence to date in support of planetary capture comes from the European Southern Observatory, which announced in 2006 the discovery of two planets (weighing 14 and 7 times Jupiter) orbiting each other without a star.

"The rogue double-planet system is the closest thing we have to a 'smoking gun' right now," said Perets. "To get more proof, we'll have to build up statistics by studying a lot of planetary systems."

Could our solar system harbor an alien world far beyond Pluto? Astronomers have looked, and haven't found anything yet.

"There's no evidence that the Sun captured a planet," said Perets. "We can rule out large planets. But there's a non-zero chance that a small world might lurk on the fringes of our solar system."

On the origin of planets at very wide orbits from the re-capture of free floating planets - Hagai B. Perets, M. B. N. Kouwenhoven
Rogue Planets Can Find Homes Around Other Stars
Universe Today | Nancy Atkinson | 2012 Apr 17

http://asterisk.apod.com/viewtopic.php?t=23704
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UT: Rogue Planets Could Drive By And Scoop Up Life

Post by bystander » Thu May 10, 2012 6:31 pm

Rogue Planets Could Drive By And Scoop Up Life
Universe Today | Jason Major | 2012 May 10
Free-floating “rogue” planets may occasionally dip into the inner Solar System, picking up dust containing organic compounds — a.k.a. the ingredients for life — and carry it back out into the galaxy, according to new research by Professor Chandra Wickramasinghe, Director of the University of Buckingham Centre for Astrobiology in the UK.

Rogue planets are thus called because they are not in orbit around a star. Either forcibly ejected from a solar system or having formed very early on in the Universe — even within a few million years after the Big Bang, the team proposes – these vagrant worlds may vastly outnumber stars. In fact, it’s been suggested there’s as much as 100,000 times more rogue planets than stars in our Milky Way galaxy alone!

Read: Rogue Planets Can Find Homes Around Other Stars

Professor Wickramasinghe — a proponent of the panspermia hypothesis whereby the ingredients for life can be transported throughout the galaxy on dust, comets, and perhaps even planets — and his team have suggested in a paper published in the journal Astrophysics and Space Science that Earth-sized rogue planets could pass through the inner Solar System, possibly as often as once every 25 million years on average. Like a cosmic drive-thru these planets could gather zodiacal dust from the plane of the Solar System during their pass, thus picking up organic compounds along the way.

The planets would then take the material gathered from one solar system and possibly bring it into another, serving as a type of interstellar cross-pollinator.

Wickramasinghe’s team propose that, by this process, there could be more life-bearing, Earth-sized planets existing between the stars than orbiting around them — a lot more. Based on their estimates there may be as much as a few hundred thousand billion such worlds in our galaxy… that’s several thousand for every star.

It will be interesting to see how this idea is received, but it definitely is an intriguing concept. As we hunt for the “Holy Grail” of life-friendly exoplanets around other stars, they may be hiding out in the darkness in numbers, in the space between.

Free-floating planets in the Milky Way outnumber stars by factors of thousands
Springer | Heidelberg | 2012 May 10

Life-bearing primordial planets in the solar vicinity - N. Chandra Wickramasinghe et al
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SAO: Capturing Planets

Post by bystander » Mon May 21, 2012 4:45 pm

Capturing Planets
Smithsonian Astrophysical Observatory
Weekly Science Update | 2012 May 11
The discovery of planets around other stars has led to the realization that alien solar systems often have bizarre features - at least they seem bizarre to us because they were so unexpected. For example, many systems have giant planets closer to their star than Mercury is to the Sun, while other have the opposite - giant planets more than ten times farther way from their star than Jupiter is from our Sun. Astronomers think they understand how planets could end up close to the star: they gradually drift in from more customary orbits. But how can planets end up so far away?

A new theoretical study by CfA astronomer Hagai Perets and his colleague proposes a possible answer: the distant planets are not part of the original stellar system - they were captured by the star. Astronomers know that there are many so-called "free floating planets" in space - planets that have been tossed out of their original solar system by a random gravitational encounter with another planet. Some of these orphan planets have recently been detected.

The scientists calculated that it would be possible for a star to capture one of these orphans if the conditions were right; namely, if the star and planet happen to pass close to each other with only a small velocity difference, and if there are no other massive bodies nearby to interfere with the "adoption." They ran a series of computer simulations to test all these and other possibilities, and they found not only that such a capture was possible, but that a star could even capture several orphan planets. In fact, they found that sometimes two free floating planets could capture one another and form a binary planet. None of these binaries has yet been seen, although some astronomers think that since Pluto and its moon Charon have such similar masses they are a binary system, although not necessarily one that was captured. The new results seem to offer a reasonable, if exotic, explanation for some of the complex planetary configurations that have been discovered, and they remind us that nature is full of surprises.

On the Origin of Planets at Very Wide Orbits from the Recapture of Free Floating Planets - Hagai B. Perets, M. B. N. Kouwenhoven (see above)

http://asterisk.apod.com/viewtopic.php?t=27466

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Know the quiet place within your heart and touch the rainbow of possibility; be
alive to the gentle breeze of communication, and please stop being such a jerk.
— Garrison Keillor